(i) Field of the Invention
The present invention relates to an organic electroluminescent panel, particularly a multicolor organic electroluminescent panel capable of emitting lights of three different wavelengths corresponding to red, green and blue colors, as well as to a process for producing the electroluminescent panel.
(ii) Description of the Prior Art
As a conventional process for producing a color organic electroluminescent panel of independent light-emission for red, green and blue colors, capable of emitting lights of different wavelengths corresponding to said three colors, there is disclosed, in JP-A-5-258859 (U.S. Pat. No. 5,294,869), a process which comprises forming a transparent electrode pattern made of ITO or the like, on a glass substrate, then placing a shadow mask made of an insulating material, on the substrate, and forming individual organic layers by utilizing the shadow mask.
According to this process, oblique vapor deposition is used for separation of three colors; that is, as shown in FIG. 6, in forming organic layers corresponding to three different colors, by vapor deposition, walls 21a and 21b of different heights are used to control the angle between the substrate and the vapor flow from vapor source and thereby a pattern of organic layers is formed. Lastly, an electrode metal is vapor-deposited in a direction normal to the ITO film 22 to form a cathode, whereby an organic electroluminescent panel is produced. In this process, however, the relative positioning of the vapor source, the substrate and the walls is very difficult; the thickness of each organic layer tends to become nonuniform; and the color separation between red, green and blue organic layers becomes insufficient. Further, the spaces emitting no light become large. Furthermore, when a large panel is produced, the geometric angle formed by the vapor source and the substrate differs between the center and the end both of the panel, making nonuniform the sizes of dots.
In conventional ordinary panel structures, when red, green and blue organic luminescent layers are formed by vapor deposition, each organic luminescent layer and each electron transport layer was formed in the size only slightly larger than each luminescent portion in each pixel; therefore, there was an organic luminescent layer-free gap between each adjacent pixels of different colors, that is, in each space 10. When a cathode material is vapor-deposited on the electron transport layers, a cathode is formed also in the organic luminescent layer-free gap of said space as shown in FIG. 7; as a result, the cathode-anode distance becomes short at each space 10, resulting in appearance of electric field concentration or electric field nonuniformity in the space 10. Therefore, when the panel was produced in a dot matrix structure, there was a problem of random appearance of current leakage or short-circuiting in a pixel. Further, electric field concentration gave rise to nonuniform generation of Joule heat during operation, which incurred, in some cases, nonuniform deterioration of luminance and generation of dark spots in the panel.
In JP-A-9-167684 is described a process for forming organic electroluminescent layers mainly by a transfer printing method. In this process, however, it is impossible to form organic electroluminescent layers without making gaps between them, unless special consideration is made.
In JP-A-7-235378 is described a process which comprises forming a layer which becomes an electron-hole recombination region, then coating a fluorescent dye, thereafter applying a heat to diffuse the dye into the recombination region layer, and forming an electron transport layer. In this process, however, since a wet method is used for the formation of the recombination region layer, the efficiency of carrier injection and the efficiency of light emission are strikingly low; and it is difficult to make uniform diffusion and concentration distribution of the fluorescent dye and accordingly it is difficult to obtain uniform luminance and pixel pitch.
The present invention has been completed in order to solve the above-mentioned problems of the prior art. The present invention is intended to provide a multicolor organic electroluminescent panel which can prevent appearance of electric field concentration and electric field nonuniformity and which gives rise to neither short-circuiting nor current leakage therein and incurs neither nonuniform deterioration of luminance nor generation of dark spots therein, and a process for producing the electroluminescent panel.
The present invention is directed to a multicolor organic electroluminescent panel having, between two kinds of electrodes facing each other wherein at least one kind is transparent or translucent, organic luminescent layers each capable of emitting a light of different wavelength corresponding to predetermined colors and an electron transport layer(s), wherein:
the organic luminescent layers are separated from each other between each adjacent pixels of different colors and the electron transport layer(s) has no gap between each adjacent pixels and is filled in each gap present between the organic luminescent layers.
The present invention is also directed to a multicolor organic electroluminescent panel having, between two kinds of electrodes facing each other wherein at least one kind is transparent or translucent, organic luminescent layers each capable of emitting a light of different wavelength corresponding to predetermined colors and electron transport layer(s), wherein:
at least either of the organic luminescent layers and the electron transport layers overlap with each other at the boundary of each adjacent pixels of different colors.
The present invention is also directed to a process for producing a multicolor organic electroluminescent panel which comprises a step of forming, on a transparent substrate, organic luminescent layers each capable of emitting a light of different wavelength corresponding to predetermined colors and a step of forming an electron transport layer(s) on the organic luminescent layers, wherein:
the organic luminescent layers are formed so as to be separated from each other between each adjacent pixels of different colors and the electron transport layer(s) is formed so as to have no gap between each adjacent pixels and be filled in each gap present between the organic luminescent layers.
The present invention is further directed to a process for producing a multicolor organic electroluminescent panel which comprises a step of forming, on a transparent substrate, organic luminescent layers each capable of emitting a light of different wavelength corresponding to predetermined colors and a step of forming an electron transport layer(s) on the organic luminescent layers, wherein:
at least either of the organic luminescent layers and the electron transport layers are formed so as to overlap with each other at the boundary of each adjacent pixels of different colors.
The present invention is yet further directed to a process for producing a multicolor organic electroluminescent panel which comprises a step of forming, on a transparent substrate, organic luminescent layers each capable of emitting a light of different wavelength corresponding to predetermined colors and a step of forming an electron transport layer(s) on the organic luminescent layers, wherein:
at least either of the organic luminescent layers and the electron transport layers are formed for each of the colors by vapor deposition through a mask having openings larger than the luminescent portions of pixels so that they contact or overlap with each other between each adjacent pixels of different colors.
The present invention yet further directed to a process for producing a multicolor organic electroluminescent panel which comprises a step of forming, on a transparent substrate, organic luminescent layers each capable of emitting a light of different wavelength corresponding to predetermined colors and a step of forming an electron transport layer(s) on the organic luminescent layers, wherein:
both the organic luminescent layers and the electron transport layers are formed for each of the colors by vapor deposition of organic luminescent layer and electron transport layer in succession through a mask having openings larger than the luminescent portions of pixels so that both the organic luminescent layers and the electron transport layers contact or overlap with each other between each adjacent pixels of different colors.